If this the case, you have to remove all references to alsa driver in /etc/modules.autoload and see /etc/modules/d/alsa. This is a new config file and it contains some example for setting up alsa driver. Take care that some drivers have a different name from the alsa 0.5 ones.

Okay, similar problem,
I have just emerged Alsa0.9 on a new system, and after the initial setup my oss sound doesn't work. On the old sys I loaded snd-pcm-oss in modules.autoload, but doing that now causes problems -> the alsa already started error. So, snd-pcm-oss and snd-mixer-oss have had to be removed from modules.autoload.

I have this in my alsa file... and also my modules.conf after 'update-modules'.
...
alias snd-card-0 snd-emu10k1
alias sound-slot-0 snd-card-0

OSS compat is not loaded at Boot time, despite the service lines above. lsmod, has no mention of any oss. If i modprobe the two files, mixer and pcm, all is fine... but I don't really want to do that every time I boot my pc.